title: Isolation and characterization of Arabidopsis halleri and Thlaspi caerulescens phytochelatin synthases.
abstract: The synthesis of phytochelatins (PC) represents a major metal and metalloid detoxification mechanism in various species. PC most likely play a role in the distribution and accumulation of Cd and possibly other metals. However, to date, no studies have investigated the phytochelatin synthase (PCS) genes and their expression in the Cd-hyperaccumulating species. We used functional screens in two yeast species to identify genes expressed by two Cd hyperaccumulators (Arabidopsis halleri and Thlaspi caerulescens) and involved in cellular Cd tolerance. As a result of these screens, PCS genes were identified for both species. PCS1 was in each case the dominating cDNA isolated. The deduced sequences of AhPCS1 and TcPCS1 are very similar to AtPCS1 and their identity is particularly high in the proposed catalytic N-terminal domain. We also identified in A. halleri and T. caerulescens orthologues of AtPCS2 that encode functional PCS. As compared to A. halleri and A. thaliana, T. caerulescens showed the lowest PCS expression. Furthermore, concentrations of PC in Cd-treated roots were the highest in A. thaliana, intermediate in A. halleri and the lowest in T. caerulescens. This mirrors the known capacity of these species to translocate Cd to the shoot, with T. caerulescens being the best translocator. Very low or undetectable concentrations of PC were measured in A. halleri and T. caerulescens shoots, contrary to A. thaliana. These results suggest that extremely efficient alternative Cd sequestration pathways in leaves of Cd hyperaccumulators prevent activation of PC synthase by Cd²⁺ ions.
authors.affiliation: Faculté des Sciences, Laboratoire de Physiologie & de Génétique moléculaire des Plantes, Université Libre de Bruxelles, Campus Plaine CP242, 1050 Brussels, Belgium.
authors.forename: Claire-Lise
authors.initials: CL
authors.lastname: Meyer
authors.forename: Daniel
authors.initials: D
authors.lastname: Peisker
authors.forename: Mikael
authors.initials: M
authors.lastname: Courbot
authors.forename: Adrian Radu
authors.initials: AR
authors.lastname: Craciun
authors.forename: Anne-Claire
authors.initials: AC
authors.lastname: Cazalé
authors.forename: Denis
authors.initials: D
authors.lastname: Desgain
authors.forename: Henk
authors.initials: H
authors.lastname: Schat
authors.forename: Stephan
authors.initials: S
authors.lastname: Clemens
authors.forename: Nathalie
authors.initials: N
authors.lastname: Verbruggen
mesh_terms: D000595:Amino Acid Sequence; D019881:Aminoacyltransferases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D001483:Base Sequence; D002104:Cadmium / Q000378:metabolism; D002614:Chelating Agents / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant; D008969:Molecular Sequence Data; D054811:Phytochelatins / Q000096:biosynthesis*; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D031227:Thlaspi / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D015032:Zinc / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D002614:Chelating Agents; D002104:Cadmium; D054811:Phytochelatins; D019881:Aminoacyltransferases; C502365:AT5G44070 protein, Arabidopsis; C502364:PCS2 protein, Arabidopsis; C093784:glutathione gamma-glutamylcysteinyltransferase; D015032:Zinc